Blender Preferences Window Size
You may want to setup your own layout configuration. 

I'd suggest: 


Open Blender
Make necessary changes you want to the windows so that you'd get to the exact screen you want every time you open the Blender. 
Press Ctrl + U {or go to top-left corner and click on File > Save Startup File > Save
Startup File (confirmation)} 
Now, close the Blender application window and try to re start the application. You'll see the applied changes to your interface.  


Something like this: 
 

You can learn ways to setup the configuration reading the documentation here: 
https://docs.blender.org/manual/en/latest/interface/window_system/screens.html 

There are tons of videos on customizing the layouts/ start-screen. One that I can recommend: 
https://www.youtube.com/watch?v=yqPJJGzqrQk 

Hope that helps!